A compact type printer of the electrophotographic method operating at low cost, accompanied with improved image performance via high resolution, has recently been desired. On the one hand, a toner having a small particle diameter has been utilized due to customer demand for the foregoing image quality.
In order to realize a compact printer at low cost, structure members of a developing apparatus and the apparatus configuration itself are to be simplified, or the number of parts are considered to be reduced. As a result, by an amount equivalent to the simplification of an apparatus, it was particularly difficult to adjust and control temperature and humidity, and process correction. Similarly to a toner transport system and a toner supply system, a toner itself was also desired to be improved in order to transport a toner smoothly. When a, toner having a small particle diameter is used for an apparatus, and the toner remains unused for a couple of days with no operation of the apparatus, the interparticle density is increased, whereby the fluidity tends to be markedly lowered, which is also called “packing”.
A technique to counter the above problem is to provide external additives, for which acicular titanium and titanium-enclosing silica are used as a method of improving toner transportability (refer to Patent Document 1, for example). It is also reported that a toner into which such external additives are added exhibits excellent image transfer and image improvement (refer to Patent Document 2, for example).
Printers designed for office use require speedy print preparation to meet the demand of an office environment. Accordingly, though the speedy charge rising capability of a toner is recently desired in order to satisfy the above demand, a toner capable of high-speed print preparation has not been acquired. In the foregoing document, for example, the improved charge rising capability via adding the external additives was disclosed, but the speedy print preparation was not addressed. Thus, it was difficult to improve the charge rising capability of a toner employing existing external additives.
Toner of a small particle diameter which results in the foregoing “packing” tends to decrease the amount of charge during no operation of the apparatus for a long period of time, whereby it is further difficult to realize the speedy print preparation. Since variation in tonal resolution are easily generated through the unstable toner supply during printing, caused by lowered toner fluidity as a result of “packing”, it was difficult to accurately read contents in graphs containing prints and recognize photographic images in which data variance is frequently shown by a gradual change of density.
In order to follow up the charge rising capability, a method of using a charge supporting member is proposed (refer to Patent Document 3), but this method is not appropriate for a low cost compact printer since an increased number of parts as well as a complicated apparatus configuration are introduced.    (Patent Document 1) Japanese Patent O.P.I. Publication No. 6-208241.    (Patent Document 2) Japanese Patent O.P.I. Publication No. 8-44103    (Patent Document 3) Japanese Patent O.P.I. Publication No. 2004-138644